Dc-to-dc power converters are widely used to supply power to electronic devices, such as computers, printers, etc. Such dc-to-dc converters come in a variety of configurations for producing a desired output voltage from a source voltage. For example, a buck or step down power converter produces an output voltage that is less than the source voltage. A typical step down converter has high conversion efficiency, is relatively simple, and requires no output transformer.
A typical step down converter, such as including the HIP 5020 converter controller made by the assignee of the present invention, is a compact integrated circuit, has high efficiency, and is easy to use. The pulse width modulation (PWM) circuit of a typical dc-to-dc converter accepts a clock signal as an input along with a signal from an error amplifier. The error amplifier, in turn, controls switching on the output current and, thus, controls the current and voltage delivered to the load.
There are many commercial applications where a relatively low dc voltage in the range of 2 to 5 volts is desired, such as for powering a microprocessor. Turning to FIG. 1, a prior art circuit 10 is illustrated and includes a conventional dc-to-dc converter 12 connected to a load in the form of a P6 Class microprocessor 13. The converter 12 is supplied power from the illustrated rechargeable battery 11. Unfortunately, the P6 Class microprocessor 13 may generate relatively large transient currents. For example, in an effort for greater energy conservation, such a microprocessor will typically switch off unused circuit portions, such as when in a sleep mode. Switching off the circuits may generate large current excess transients. Moreover, when the microprocessor awakes from the sleep mode, large current demand transients on the order of 1 amp/nanosecond may be generated by the microprocessor 13.
A typical dc-to-dc converter 12 may take from 5 to 100 microseconds to build up current, in part, because of the relative slowness of the pulse width modulation control. As illustrated in FIG. 1, a relatively large number of expensive electrolytic capacitors 14, such as tantalum capacitors, are used to store charge and supply this current. In the illustrated embodiment, eight capacitors 14 are used. Besides being relatively expensive, the capacitors each may have a fairly large footprint 15 and volume, and thereby collectively take up valuable limited real estate within a notebook or other personal computer, for example.